i know electricals are more accurate, but what is the difference in istallation?
ex: for a mechanical oil press guage, do you have to run a small oil line to the guage?

 

you got it... depending on type of gauge oil/temp/etc, the mechanical normally carries the fluid to to gauge to do its thing... an example is the fuel pressure gauge where they insist that the gauge be installed on the exterior of the vehicle for safety reasons (aka. hood)... whereas the electrical utilizes a sender unit that processes the info and send it to the guage as an electrical signal that the gauge interprets...